An unclassified member of the bacterial family Pasteurellaceae has been isolated from cases of enteritis, conjunctivitis, and abscessation in a colony of golden hamsters (Mesocricetus auratus). This bacterium is a member of the Haemophilus/Pasteurella group, based on preliminary biochemical testing. It may represent a new species, but additional studies such as DNA hybridization will help to define the taxonomic position. Three golden hamster strains are maintained in the colony - N:Syr (Syrian), N:M70 (Murphy), and N:LSH/TrN. The Haemophilus/Pasteurella group bacterium has been isolated from all strains. Both clinically ill and healthy adult hamsters representing all strains have been examined for gross and microscopic abnormalities, identification of gastrointestinal parasites, characterization of intestinal microflora, and identification of pathogenic bacteria at sites of inflammation. Syrian hamsters from outside the colony have been used to determine the relative pathogenicity of the Haemophilus/Pasteurella group bacterium. Various routes of inoculation and doses of bacteria have been combined with clinical observations and post-mortem studies. This unique bacterial species in the Haemophilus/Pasteurella group is widespread in the NIH hamster colony. It is associated with disease processes which may interfere with the research activities of the NIH scientists. This study will help define the lesions produced, extent of the disease in the colony, and will result in the development of appropriate techniques to rid the colony of the infection and thus improve the health of animals used by NIH scientists.